This invention relates to a tool holder for a hand held electrically powered hammer and to a hand held electrically powered hammer incorporating such a tool holder. In particular this invention relates to tool holders for demolition hammers.
Such hammers generally comprise a housing within which is located an electric motor and a gear arrangement for converting the rotary drive of the motor to a reciprocating drive to drive a piston within a hollow spindle or cylinder, which spindle is located within the hammer housing. A ram is located in front of the piston within the spindle so as, in normal operating conditions, to form a closed air cushion within the spindle between the piston and the ram. The reciprocation of the piston reciprocatingly drives the ram via the air cushion. A hollow piston arrangement may be used, as is well known in the art. A beatpiece is generally located within the spindle and transmits repeated impacts that it receives from the ram to a tool or bit releaseably mounted for limited reciprocation in front of the beatpiece in a tool holder portion. The impacts on the tool or bit are transmitted to a workpiece against which the tool or bit is pressed in order to break up or make a bore in the workpiece.
Some hammers may also be employed in combination impact and drilling mode in which the tool holder, and hence the tool inserted therein, will be caused to rotate at the same time as the tool is struck by the beatpiece. The present invention is also applicable to such hammers.
A common form of chiselling tool or bit, for performing heavy duty work is a hex-shanked tool or bit. The portion of the tool which is locked within the tool holder of the hammer has a hexagonal transverse cross-section. The bore in the tool holder which receives the hexagonal shank portion generally has a corresponding hexagonal transverse cross-section and so the tool is non-rotatably fitted within the tool holder. The hexagonal portion is formed on one of its flats with an axially extending groove which is closed at both its ends. The hex-shanked tool can be locked within the tool holder to enable limited reciprocation of the tool within the tool holder. Traditionally, a cross bolt arrangement is used to lock the tool within the tool holder. The bolt extends tangentially of the toolholder to engage the groove in the tool. The bolt can be retracted or pivoted outwardly to allow insertion or removal of the tool.
An alternative to a hex-shanked tool or bit for use on hammers is an SDS-type tool or bit. The SDS-type tools have a tool shank which is provided with irregularly positioned axially extending grooves, open at their rearward ends which grooves co-operate with radially inwardly extending splines in the bore of the tool holder. Thus, the tool is non-rotatably fitted within the tool holder. In addition the SDS-type tools have two axially extending grooves which are closed at their ends and which are each engageable by a locking body in order to lock the tool within the tool holder so as to allow limited reciprocation of the tool within the tool holder. Tool holders for SDS-type tools generally have one or two radially shiftable locking bodies which can be releaseably locked within one of the, or each, groove of a tool inserted into the tool holder.
It is an aim with tool holders for hammers to have a simple, compact and ergonomic design in which the locking body can move between its radially inward locked position and its radially outward unlocked position smoothly. It is also advantageous to provide automatic locking of a tool within the tool holder, to enable the tool to be locked in the tool holder automatically by simply pushing the tool into the tool holder, without manually actuating the tool holder.